French riot police arrested 27 people after running battles with dozens of hooded and masked youths in downtown Paris's Place de la Republique overnight, after a day of separate protest marches over labor reform that were also marked by violence.

In the early morning, police moved in to clear out a group of around 150 youths who refused to quit the vast open square. It has been occupied daily for the past month by mostly peaceful sit-in protesters.

The evacuation followed running battles between police and youths who set cars on fire and hurled lumps of concrete and cobblestones ripped up from the streets, the Interior Ministry said in a statement.

The late-night clashes followed a day of street marches in which dozens more were arrested. The violence took place on the fringes of rallies involving tens of thousands of people protesting over a law to make hiring and firing easier. In France, labor protection is sacrosanct and unemployment above 10 percent.

In all, police reported 124 arrests during Thursday's protests and demonstrations, in which 24 police were injured, one in serious condition after a skull-cracking blow from a paving block.

Paris police prefect Michel Cadot said highly organized groups were behind the violence that has developed despite the state of emergency rules imposed since the deadly Islamist attacks of last November.

The French government has condemned the violence. But with just a year to elections, seems keen so far to waive the blanket curfew option it has under the state of emergency system.